The present invention concerns an apparatus for connecting a wire to a contact element and a method of operating such an apparatus.
An apparatus of that kind is known for example from the present applicants' German patent specification No 40 39 051. Such crimping tools, but also other situations of use, require drive means which, in the cycle consisting of starting, crimping and braking, can initiate braking operations in particular in a very short time.
Usually such a braking procedure is effected mechanically. However, particularly in the case of apparatuses which are operated in a continuous mode, that results in severe wear and thus has a detrimental effect on the useful life.
In addition it would be theoretically possible for the drive motor to be braked by operating in a generator mode. It will be noted that if the drive motor used is an asynchronous machine, the arrangement must provide for direct-current excitation by feeding a direct current into the working winding so that a braking effect occurs. As however the braking current which is required for that purpose is high and as there is not a sufficient cooling time due to the high cycle rate of the crimping apparatus, there is the risk of the motor burning out. For that reason alone generator-mode braking has hitherto not been adopted.
In addition however such a braking procedure would also suffer from the disadvantage of inadequate positional accuracy which makes it unsuitable for use in crimping apparatuses: as a, usually single-phase, asynchronous motor has an elliptical rotating field and thus the magnetic flux fluctuates in the direction of rotation, the field is not suitable for a braking mode which gives accurate positioning. On the contrary that could result in overrunning on the part of the apparatus in question, or another inaccurate braking performance.